To foster sustainable, low-emission development, many countries are establishing ambitious renewable energy targets for their electricity supply. Because solar and wind tend to be more variable and uncertain than conventional sources, meeting these targets will involve changes to power system planning and operations. Grid integration is the practice of developing efficient ways to deliver variable renewable energy (VRE) to the grid. Good integration methods maximize the cost effectiveness of incorporating VRE into the power system while maintaining or increasing system stability and reliability.

Wind and solar are inherently more variable and uncertain than the traditional dispatchable thermal and hydro generators that have historically provided a majority of grid-supplied electricity. The unique characteristics of variable renewable energy (VRE) resources have resulted in many misperceptions regarding their contribution to a low-cost and reliable power grid.

Power system planning methods and processes can evolve to address the unique characteristics of variable renewable energy (VRE). This brief presents an overview of the analyses involved in traditional power system planning, and describes the changes required to plan for higher levels of VRE integration.

Countries around the world have established ambitious targets for increasing the contribution of renewable energy toward meeting their national energy demand. At low penetrations of wind and solar (e.g., below 5%–10% of annual electric demand), impacts to the power system are likely to be minimal. However, as the proportion of variable renewable energy (VRE) connected to the grid increases, power system planners will increasingly need to evaluate and manage the impact of increased variability and uncertainty on system operations. They will also need to ensure that the policy and regulatory environment offers sufficient certainty and revenue streams to encourage investment in new VRE generation. To address these needs, power system planners can take several steps to align targets and incentives with grid integration considerations.

An important aspect of power system planning is ensuring that adequate generation capacity exists to meet electricity demand during all hours of the year. Mechanical failures, planned maintenance, or lack of on-demand generating resources (especially for variable renewable resources) may leave a power system with insufficient capacity to meet demand. Grid planners project future peak demand patterns and estimate the relative contribution of each generator towards achieving a reliable supply of energy. When generating during peak demand periods, variable renewable energy (VRE) such as wind or solar PV provides capacity value to the system. By providing capacity value, VRE can help to defer capital investments in traditional generation and transmission infrastructure.

Coordinating balancing area operation can promote more cost and resource efficient integration of variable renewable energy (VRE), such as wind and solar, into power systems. This efficiency is achieved by sharing or coordinating balancing resources and operating reserves across larger geographic boundaries.

Operational flexibility refers to the ability of a power system to respond to changes in electricity demand and generation. Flexibility is particularly important for power systems that integrate high levels of solar and wind, whose power outputs can be variable and uncertain, creating a fluctuating supply.

A grid integration study is an analytical framework used to evaluate a power system with high penetration levels of variable renewable energy (VRE). A grid integration study simulates the operation of the power system under different VRE scenarios, identifying reliability constraints and evaluating the cost of actions to alleviate those constraints. These VRE scenarios establish where, how much, and over what timeframe to build generation and transmission capacity, ideally capturing the spatial diversity benefits of wind and solar resources. The results help build confidence among policymakers, system operators, and investors to move forward with plans to increase the amount of VRE on the grid. High quality data are critical to robust and reliable grid integration studies.

Forecasting is a crucial and cost-effective tool for integratingvariable renewable energy (VRE)resources such as wind and solar into power systems. This fact sheet reviews the key terms and methods for operational forecasting of variable renewable energy generation.

Distributed, grid-connected photovoltaic (PV) solar power poses a unique set of benefits and challenges. This brief overviews common technical impacts of PV on electric distribution systems and utility operations (as distinct from other utility concerns such as tariffs, rates, and billing), as well as emerging strategies for successfully managing some of the priority issues.

Power purchase agreements (PPAs) represent one of many institutional tools that power systems can use to improve grid services from variable renewable energy (VRE) generators. This fact sheet introduces the concept of PPAs for VRE generators and provides a brief summary of key PPA components that can facilitate VRE generators to enhance grid stability and serve as a source of power system flexibility.

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Interested in partnering through Greening the Grid to receive technical assistance on grid integration? Please contact us (greeningthegrid@nrel.gov) to learn more and explore opportunities for collaboration.

Greening the Grid is supported by the U.S. Agency for International Development (USAID), and is managed through the USAID-NREL Partnership, which addresses critical aspects of advanced energy systems including grid modernization, distributed energy resources and storage, power sector resilience, and the data and analytical tools needed to support them.